1. Field of the Invention
The present invention generally relates to an apparatus for melting, refining and processing metals, for example, the process of steelmaking in an electric arc furnace (EAF), and more particularly, to a reusable lance with a consumable refractory tip for the injection of an metallurgical, process gases and/or particulate materials used in such proceses.
2. Description of Background Art
The process of steelmaking in electric arc furnaces has evolved such that the application of oxidizing gases, preferably pure oxygen, or other metallurgical gases including nitrogen, methane, carbon dioxide, etc.; particulate materials such as carbon and coal powders, direct reduced iron (DRI), iron carbide, etc.; and/or combinations of these gases and or particulate materials, is now normally used in the melting, refining and other processing steps of making steel in an electric arc furnace.
In general, oxygen may be used for multiple purposes at different points in the melting and refining process in EAF steelmaking. For example, initially it may be used to add heat by combusting carbon and other oxidizable materials and to cut scrap during the preheating phase of a melt. Oxygen has also been used to assist in the formation of foamy slag during or at the end of the melting phase, and to decarburize the molten bath during refining. It is conventional to use oxygen for the post combustion oxidation of CO in any phase of the steelmaking process.
Normally, the oxygen for all of these subprocesses is introduced as a high velocity jet through a pipe generally termed, an oxygen lance. Typical lance implementations have been accomplished by one of two methods, either by one or more moveable consumable oxygen lances which may be submerged in the molten steel bath, or one or more moveable water cooled oxygen lances which are positioned above the bath.
In normal operation, the water cooled oxygen lance is first introduced into the EAF and then gradually moved to a position by a manipulator where the end or tip of the lance is very close to the surface of the bath. The discharge velocity and angle of the oxygen stream is carefully chosen to allow the stream of oxygen to penetrate the slag and the melt to react efficiently with the iron-carbon melt. If the angle is too shallow or the pressure too low, then the oxygen will not penetrate the molten metal bath and efficiently decarburize the melt. On the other hand, if the angle is too steep or the pressure to high, then the metal in the bath may detrimentally splash on the EAF walls and electrodes. Conventionally, the water cooled oxygen lances have used supersonic nozzles, typically of the De Laval type, to produce the high velocity gases needed to penetrate the surface of the melt.
The water cooled lances are gaining in popularity because they are generally less expensive than consumable lances because one can replace the lance tips by welding and reuse most of the lance body. But the water cooled lances tips are relatively complex and, even though not directly in contact with the melt, need to be replaced fairly often because of the harsh environment. Further water cooled lances are somewhat less efficient in the delivery of the oxidizing gas to the reaction zone. This is because care must be taken to not touch or submerge the lance tip in the bath, or even place it where it could be consistently splashed with hot melt. Because the lance can not be brought into the reaction zone, the result is extra oxidizing gas within the furnace. Extra oxygen in the furnace contributes to the unnecessary oxidation of the electrodes, wall panels, etc.
Consumable lances, while being able to be submerged directly in the molten bath to efficiently place gases and materials in a reaction zone, do not have the control of gas and particulate flow rates like water cooled lances with their nozzles. The consumable lance must always be watched by an operator to make sure its positioning and feed rate are correct as it is fed into the bath because different environments consume the lance at different rates. Additionally, the amount of injected gas or particulate material is hard to determine because the operator does not know the exact depth of the tip or the amount of gases being injected at a particular spot. These variables make gas and materials lancing with a consumable lance an art and the results difficult to repeat predictably from batch to batch.
Refractory materials, such as ceramics and the like, have been used in EAFs to provide oxygen and other metallurgical gases from the bottom of the melt by building tuyeres into the base of the furnace. The gases are then released through the tuyeres and bubble up through the bath to produce chemical reactions with the metal. While the refractory materials used in the tuyeres are relatively long lasting in the harsh environment of the EAF, they are hard to form and manipulate into shapes. A disadvantage of the tuyeres is that their presence requires extensive maintenance of the bottom shell, the necessity of a spare bottom shell, and the expense of changing the bottom shells every 2-3 weeks.
Refractory covered lances used for BOF steelmaking have been cumbersome straight lances lowered vertically through the roof or top of a steel making vessel. These lances because of their weight and size are not very useful to reach or be positioned for effective injection in an EAF. For example, they might bend or break under their own weight if mounted substantially horizontally.
Therefore, there is a need for a reusable injection lance for gases, particulate materials or combinations thereof which combines the advantages of both types of lances and is relatively inexpensive and easy to use.
There is also a need for an injection lance which is adapted to be efficiently positioned in the reaction zone for steelmaking in an EAF.